1. Field of the Invention
This invention relates to a viewfinder device and more particularly to a display of information within a visual field of a viewfinder in an image pickup apparatus such as a camera or the like.
2. Description of the Related Art
Image pickup apparatuses such as cameras or the like have heretofore been arranged to display, within a viewfinder, information of various kinds for taking pictures, including, among others, a distance measurement mark indicating a distance measuring range. For making such information displays, many methods have been proposed and put into practice. According to these conventional methods, the patterns of display information are formed by vapor deposition on a transparent member made of glass or an acrylic resin or by combining fine wedge-shaped prisms. Meanwhile, a camera information mark display device arranged to use a hologram has been proposed in Japanese Laid-Open Patent Application No. SHO 53-32048.
To enable the display information to be visible along with an object image, the conventional viewfinder device is arranged to have a pattern plane which has the patternized display information formed thereon arranged either on the image forming plane of an objective lens or near to a plane conjugate to it. The pattern plane having the display information is positioned to coincide with the diopter of a viewfinder optical system.
However, since the position of the information display member is thus arranged to coincide with the diopter of the viewfinder, if any dust, a stain or the like comes to stick to this member, the stain or the like would show in an enlarged state as the eyepiece of the viewfinder optical system acts as a magnifier.
In view of this problem, it is desirable to have a free (vacant) space without any optical part on the image forming plane of the objective lens or near to its conjugate plane, i.e., at a place which coincides with the diopter of the viewfinder. However, it has been difficult to realize such an arrangement.
Meanwhile, many cameras of the kind having a so-called panorama mode have recently been proposed. They are arranged to give a laterally long picture by partly trimming an image pickup (or photo-taking) plane to change its aspect ratio from 4:3 to, for example, 36:13.
Generally, it is desirable that a camera is arranged to give, by the visual field of a viewfinder, a sight-taking range corresponding to the range of a picture to be actually taken. To meet this requirement, the camera of the kind having the panorama mode is arranged such that, when the image pickup plane is narrowed by inserting a photo-taking range limiting member into a photo-taking system so as to switch an ordinary mode over to the panorama mode for taking a panoramic picture, the viewfinder field is also narrowed by arranging a light shielding member to partly shield the viewfinder system from light to give a laterally long viewfinder field.
In the case of the conventional camera of the kind having the panorama mode, the light shielding member is arranged near the image forming plane of the viewfinder to be retractably insertable to make the viewfinder field laterally long in taking a sight for a panorama shot.
However, with the light shielding member thus arranged to be insertable and retractable, dust, dirt or the like tends to stick to the image forming plane of the viewfinder to make the viewfinder field dirty. Besides, the dust or the dirt tends to be sighted at the same diopter as an image formed within the viewfinder.